Device for showing tensile stress

ABSTRACT

In this device for indicating ( 10 ) pretensioning forces in a tensioning element ( 7 ), such as tie-down straps or tie-down ropes, the spring surrounds the tie bolt ( 3 ) which is located on the loop of the tie-down strap, and in response to weak forces describes a path ( 6 ) which is easily visible. The combination of two components which differ in shape allows the spring ( 1 ) to maintain its shape and spring constant. As a result, the pretensioning force is indicated directly, yet the spring is not subject to an additional load under high tensions but is protected by positive engagement.

RELATED APPLICATIONS

This application is a U.S. national stage application under 35 U.S.C.§371 of international application PCT/CH2003/000385 filed Jun. 13, 2003,which claims priority under 35 U.S.C. §119 of Switzerland applicationnumber 1536/02 filed Sep. 10, 2002.

TECHNICAL FIELD

The invention relates to a device for indicating tension in a tensioningelement.

BACKGROUND

Load indicators have been disclosed and described in GB 2 255 109 Ahaving a closed grommet thimble, as well as in GB 2 223 102 A having atype of strain gauge.

Also known as disclosed in EP 0984 873 B1 is a one-piece load indicatorin which the tensile forces can be determined by the variable distanceof the leg ends of a spring which takes the form of a grommet thimble.Here the spring encloses a tie bolt which is located within a loop ofthe lashing-down strap and also describes a path which is easilydiscernible visually under small loads.

A disadvantage of this approach is that under high tensile forces theshape of the spring changes geometrically such that this increased forceis no longer discernible visually but must be measured using anadditional amplification.

All known measuring devices and load indicators of this type are locatedinside the loop of the tie-down strap or lifting sling. Load indicatorsof the same type and for the same technical means can be attachedexternally, thereby pressing on the outer faces of the loop. In thiscase, the inner faces of the loop are in contact at zero tension and arethen forced further apart as the tension increases, in other words,exhibit a reversed functional principle.

The goal of the known load indicators is to measure the entire range ofthe load, and ought therefore to have the ability to accommodate bothlow and high forces through the spring force. In the existing devices,high forces are accommodated by using a heavy material or by a smallmovement in the spring elements. In order to be able to measure the lowforces that occur in response to a pretension, a weak spring istherefore required which is at the same time able to withstand a hightensile force. Practical experience has demonstrated that weak springsundergo changes in shape when overtensioned, thereby displayingincorrect values from that point on. In solving the task at hand, theapproach is therefore to limit oneself to the tension and to ignore anyforces exceeding this value.

SUMMARY OF THE INVENTION

The goal of the invention is to design a pretension indicator forindicating tension in a tensioning element such that a result isdisplayed in response to weak forces, and that the geometry of thespring, and thus the spring constant, is preserved when high forces areapplied, and such that the movement of the spring is precisely limitedto the range of the specified force. The terms spring constant andspring rate refer to properties of the element, specifically, springthickness and spring geometry.

The principal application of this device relates to securing a load,enabling the user to read off the tension generated in order toimplement an appropriate tie-down of the load. When a load settles,there can also be a loss of the pretension which can also be read fromthis indicator.

This goal is achieved according to the invention disclosed herein. Thesolution is based on a combination of two elements which areinteractively linked, wherein, on the one hand, small forces aredisplayed in the tensioned system and, on the other hand, the allowablepretension is indicated by a positive-engaging end position. The springconstant of the spring is dimensioned such that the force to be detectedis directly readable. In order to ensure that the spring does not changeshape when this force is exceeded, the path of the spring is restrictedby a formed piece. The positive engagement of the elastic spring withthe elastic formed piece is capable of accommodating a multiple of thedisplayed force. By exploiting the different properties of thesecomponents, the combination of two or more components allows for bothsimplified fabrication and tolerance in the fabrication technique byincorporating prefabricated components in the production process. Thefunction of each individual component is thus restricted to an essentialrange, thereby ensuring that its function is performed in an optimalmanner. The attachment of additional functions does not overload theindividual component; instead, these functions can be reliablyimplemented using the material which is readily able to take on thisfunction.

The following discussion explains the invention in more detail based onspecific embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the functional principle of the pretension indicator havinga pressure-controlled deformable formed piece;

FIG. 2 shows the functional principle of the pretension indicator havinga dimensionally stable formed piece;

FIG. 3 shows a variant of an additional spring which presses thedimensional indicator onto the legs of the spring, and displaces thespring rearward when under tension;

FIG. 4 shows a variant of an elastic formed piece which deflects thedimensional indicator;

FIG. 5 shows a variant of a loose combination which provides a displayon the side;

FIG. 6 shows a positive-engaging component in the form of aninjection-molded variant with an additional centering means.

DETAILED DESCRIPTION

FIG. 1 shows a spring (1) which surrounds a deformable formed piece (5)and which expands the inner sides of the loop (2) when under zerotension. Spring (1) and formed piece (5) form a unit such that the twoelements perform the same movements. Under tensile load from thetensioning element (7) through the bolt (3), the inner sides of loop (2)press on the combination of spring (1) and formed piece (5), and movelegs (5 a) and (5 b) of formed piece (5) towards each other. Once theallowable pretension has been reached, end position (8), that is, legs(5 a) and (5 b) of formed piece (5), contact each other in a positiveengaging manner such that no further movement of spring (1) and formedpiece (5) is possible. The pretension attained is now easily read viadimensional indicator (10).

FIG. 2 shows a spring (1) having a dimensionally stable formed piece(5.1). In this design, the tensile load is indicated exclusively bydimensional indicator (6) in response to the spring force of spring (1)acting through the legs (4) of the spring. Here again, due to thepositive engagement of spring (1) and formed piece (5.1) when endposition (8) is reached, formed piece (1) prevents any overtensioning ofspring (1).

FIG. 3 shows a load indicator in which under tensile load the leg endsof the spring (1.1) move the indicating element (9) horizontally againsta spring onto the formed piece (5.2) in the direction of bolt (3). Thespring force here can be set for the specific maximum pretension.

FIG. 4 shows a load indicator in which the leg ends of the spring (1.2)press against an elastic formed part (5.3), thereby moving indicatingelement (9) through a tapering gap in the direction of bolt (3).

FIG. 5 shows the same functional principle, but with a side indicatorwhich displaces the indicating element (9) transversely out of formedpiece (5.4).

FIG. 6 shows a formed piece (5.5) in the form of an injection-moldedpiece having an additional centering means (11), which piece can beemployed as in FIG. 2.

1. Device for indicating tension in tension means, the devicecomprising: a spring which is reversely curved to form a closed end andtwo opposed legs extending from the closed end such that in use thespring is placed around a rigid web which forms a connection between astrap and tension means, and is surrounded in a streamlined shape by aformed loop of the strap; wherein the device allows for a recoverabledeformation of the spring under tension and for a scale on which thetension can be read; a formed piece with a shape to be placed around therigid web with the spring surrounding the formed piece at least in thebite of the loop at the closed end of the spring, the spring beingcombined with the formed piece in a positively engaging manner such thatthe tension of the tension means deforms the spring up to an endposition determined by the formed piece within a lower range, and suchthat the tension does not further deform the spring in a second upperrange of the tension since the spring contacts the formed piece in theend position—with the result that there is no overtension, and thus nochange in the spring constant of the spring and in a predeterminedindication range.
 2. Device according to claim 1, wherein thecombination of the spring and the formed piece is a device in which theindividual parts are both rigidly anchored.
 3. Device according to claim1, wherein the formed piece has two legs and is deformable in apressure-dependent manner until reaching the positive-engaging endposition, the formed piece following the movement of the spring, andthat based on the changing position of the two legs of the formed piecethe respective pretensioning force is readable by means of a dimensionalindicator.
 4. Device according to claim 1, wherein the formed piece isdesigned to be dimensionally stable independently of the pressure. 5.Device according to claim 1, wherein the spring and the formed piece arefabricated out of different materials.
 6. Device according to claim 1,wherein the spring encloses the formed piece, so as to bring about arigid anchoring between the two components.
 7. Device according to claim1, wherein the formed piece includes dimensional indicators which areone of directly engraved or mounted on the formed piece as separatecomponents.
 8. Device according to claim 1, wherein the formed piece hasmounted thereon a movable component which is displaced along a track bythe motion of the spring so as to produce an expanded indication range.9. Use of the device according to claim 1 for tension means selectedfrom the group consisting of ratchets and shackles.
 10. Device accordingto claim 1, wherein the combination of the spring and the formed pieceis a device in which the individual parts are both loose.
 11. Deviceaccording to claim 5, wherein the spring and the formed piece arefabricated out of, respectively, spring steel and plastic.